Over 1.5 million middle school girls in the U.S. are overweight or at risk for becoming overweight. The 10-year NHLBI Growth and Health Study showed that increases in girls'body mass index (BMI) and adiposity were related to a decrease in moderate to vigorous physical activity (MVPA). A sharp decline in girls'MVPA occurs during middle school. The Cochrane Collaboration 2005 review of interventions for preventing obesity in children underscored the need to simultaneously address individual behavior change and the environment in interventions to increase MVPA. The purpose of this study is to test the feasibility of and obtain preliminary evidence of efficacy for a 6-month "Girls on the Move" intervention (guided by the Health Promotion Model and Social Cognitive Theory). The intervention involves motivational, individually tailored counseling plus after- school physical activity (PA) to increase MVPA and cardiovascular (CV) fitness, as well as improve body composition and cognition and affective responses related to MVPA among 6th-grade girls. Specifically, it consists of a 90-minute after-school PA Club that includes MVPA and 6 one-on-one monthly motivational, individually tailored counseling sessions with a registered (school) nurse during the school day to support each girl's continued MVPA. Applying the motivational interviewing communication style, the school nurse will individually tailor the counseling based upon each girl's key responses gleaned from computerized questionnaires assessing cognitive and affective variables related to MVPA. One middle school will be randomly assigned to receive the intervention and another to serve as attention control. School nurses have had limited involvement in school-based PA interventions to date. Our study offers an innovative approach for acquiring essential evidence regarding nurse counseling as a means for assisting girls to increase and maintain MVPA. If successful, this intervention can be translated to other programs (e.g., diabetic education and weight reduction). Specific aims are: 1. Evaluate the feasibility of the intervention related to (1) girls'participation;(2) adherence to protocols;and (3) user and provider (nurse and PA Club instructors) satisfaction. 2. Explore if participants in the intervention group, compared to those in the control group, show improvement in the primary outcome of minutes of MVPA (measured by accelerometer), and also secondary outcomes of self-report of MVPA, CV fitness, BMI, percent body fat, and waist circumference at 6 months. 3. Explore if the primary outcome is mediated by cognitive (perceived benefits of PA, perceived barriers to PA, PA self-efficacy, social support, norms, models) and affective (enjoyment of PA) variables. 4. Explore if participants in the intervention group, compared to those in the control group, have greater minutes of MVPA at 7 months. PUBLIC HEALTH RELEVANCE: Our novel, comprehensive, and theory-driven intervention for middle school girls includes motivational, individually tailored counseling from a school nurse and an opportunity for physical activity at their school. This approach addresses Healthy People 2010 objectives to improve the health of youth by assisting girls to achieve national recommendations for moderate to vigorous physical activity.